The present invention relates generally to the field of electrical switchboards and panelboards having vertical bus bars, and more particularly to a bus brace comb assembly used to hold the bus bars in place against magnetic forces associated with short circuit currents in the switchboards and panelboards.
Switchgear assemblies, switchboards and panelboards are general terms which cover metal enclosures, housing switching and interrupting devices such as fuses, and circuit breakers, along with associated control, instrumentation and metering devices. Such assemblies typically include associated bus bars, interconnections and supporting structures used for the distribution of electrical power. Low voltage switchgear and switchboards operate at voltages up to 600 volts and with continuous currents up to 5000 amps or higher. Such devices are also designed to withstand short circuit currents ranging up to 200,000 amps (3 phase rms symmetrical).
Typical switchgear equipment is composed of a lineup of several metal enclosed sections. Each section may have several circuit breakers stacked one above the other vertically in the front of the section with each breaker being enclosed in its own metal compartment. Each section has a vertical or section bus which supplies current to the breakers within the section via short horizontal branch buses. The vertical bus bars in each section are supplied with current by a horizontal main bus bar that runs through the lineup of metal enclosed sections. A typical arrangement includes bus bars for each electrical phase of a multiple phase system which may include three power phases and a neutral.
The vertical or section buses described above must be braced to withstand the magnetic forces created by the short circuit currents that pass through the switchgear during a short circuit fault. High short-circuit current levels in the bus bars create conditions that require extensive bracing. This makes high short-circuit rated designs more expensive to build in terms of material and labor and additional bracing often limits the combination of breakers that can be put in a switchgear or panelboard assembly.
Thus, there is a need for a bus bar brace assembly that provides sufficient strength to withstand magnetic forces associated with short-circuit currents in the switchgear assembly. There is further need for a switchgear assembly that includes channel bus bars for each electric power phase and for supporting such channel bus bars in the manner to withstand magnetic forces associated with a short circuit current in the switchgear assembly. There is a further need for a bus brace comb assembly that provides for a compact arrangement of channel bus bars within a switchgear assembly and allows for additional insulating barriers between the channel buses of each electrical power phase of the switchgear assembly.
One embodiment of the invention relates to a bus brace comb assembly for use in a switchgear assembly. The switchgear assembly has a channel bus bar for conveying electrical current in each phase of the switchgear assembly. The bus brace comb assembly holds the bus bar in place against magnetic forces associated with short-circuit currents in the switchgear bus bar. The bus brace comb assembly comprises a front comb assembly including a first bus clip configured to position the bus bar and a front brace coupled to the bus clip. A rear comb assembly including an interlock clamp configured to engage the channel bus bar and a second bus clip secured to the interlock clamp with a fastener and a rear brace coupled to the interlock clamp/bus clip assembly. A flange of the channel bus bar is pinched between the rear brace and the interlock clamp/bus clip assembly to secure the channel bus bar in the switchgear assembly. Another embodiment includes a third bus clip a spaced distance from the first bus clip and coupled to the front brace. Another embodiment of the bus brace comb assembly provides E-shaped bus clips. An insulation cover can be provided over one of the front comb assembly and rear comb assemblies.
Another embodiment provides a switchgear assembly which includes a channel bus bar for each electric power phase and for conveying electric current. The channel bus bars are maintained in position by a bus brace comb assembly embraced against magnetic forces associated with short-circuit currents in the switchgear bus bars by the bus brace comb. The bus brace comb assembly comprises a front comb assembly including a first bus clip configured to position the bus bar and a front brace coupled to the bus clip. A rear comb assembly including an interlock clamp is configured to engage the channel bus bar and a second bus clip secured to the interlock clamp with a fastener. A rear brace is coupled to the interlock clamp/bus clip assembly, wherein a flange of the channel bus bar is pinched between the rear brace and the interlock clamp/bus clip assembly to secure the channel bus bar. Another embodiment of the switchgear assembly includes a third bus clip a spaced distance from the first bus clip and coupled to the front brace. Another embodiment of the switchgear assembly provides E-shaped bus clips. An insulation cover can be coupled to one of the front comb assembly and rear comb assembly of the switchgear assembly.
There is also provided a method of securing and positioning channel bus bars in each power phase of the switchgear assembly with a bus brace comb assembly. The bus brace comb assembly has a front comb assembly and a rear comb assembly. The method comprises the steps of positioning each channel bus bar and a bus clip of the front comb assembly. Installing an interlock clamp to couple with at least one flange of a channel bus bar in each power phase. Fastening another bus clip to the interlock clamp. Coupling a rear brace to each bus clip/interlock clamp assembly, wherein the flange of the channel bus bar is pinched in the interlock clamp/bus clip assembly to secure the channel bus bar. Another embodiment includes the step of coupling a front brace to the bus clip of the front comb assembly. Another embodiment of the method includes the step of installing an insulation cover on the bus brace comb assembly.